The amount and quality of dietary protein has been shown in earlier studies to influence the incidence of pathological lesions associated with severe hypertension in certain rat models. Specifically low protein diets resulted in a greater number of cerebral lesions and stroke in the stroke-prone spontaneously hypertensive rat (SHR-SP). The current study is an attempt to understand the biochemical basis for the protective effect of dietary protein. SHR-SP were maintained on natural diets containing different levels of protein, some of which were supplemented with methionine, and various aspect of membrane calcium metabolism were examined. Preliminary results suggest that sarcoplasmic reticulum isolated from heart has greater Ca++ binding capacity when animals are maintained on a high protein diet. Likewise there was an apparent slight increase in Ca++ ATPase of this organelle in animals receiving the higher protein diet. Pathological examination of the tissues also revealed fewer lesions in the rats supplemented with protein.